First I cut the shape out of MDF 

I Sculpted on a layer of oil based clay for the lower raised portion.

Mounted on a backboard and boxed up for moulding.

Pouring in the silicone.

Laying up some fibreglass and resin in the mould.

Filling the blemishes to get a smooth finish.

A coat of primer.

Another round of filling and sanding.

The finished master.

I moulded up the cod and cast a positive silicone piece.  I then made a negative plaster mould which I poured the liquid latex in.  

The final latex piece.

To mount the cod on the suit, install a 15cm (6 inch) trouser zip in the mesh suit as a fly (only use a good quality YKK zip, the cheap ones WILL fail).

Using some strapping off an old backpack and some denim patches, I stitched up these parts 

Using liquid latex as a glue, I glued the pieces on to my cod. the denim patches soak up the latex where the strapping would not.

Then I put a snap base in the back of my suit just under my zip in the lower back. I used the denim disk as a washer to stop it rubbing through the mesh. It does not fit in dead centre because of the stitched seam, but off to one side slightly is fine.

Then I stitched on the cod to the suit by the two straps making a hinge. Don’t forget to melt the ends of the straps before you stitch them on to the suit to stop them fraying 

Then I threaded through a length of thick black elastic cord and sewed the ends together. Again I melted the tips to stop fraying

And here is the back view where the snap attaches. So you need to keep the elastic taught under the crotch to keep the cod pulled against your body, but you don’t want it too tight or it will distort the cod and be uncomfortable.